This invention relates to an air purifying filter having a modified enzyme immobilized on a surface of a carrier. The invention particularly relates to an air purifying filter having an enzyme immobilized on a surface of a HEPA filter which is composed of boron-silica glass fibers not rendered to be water repellent, ion-exchange fibers having functional groups, or boron-silica glass fibers coated with a polymer having functional groups.
Various air purifiers (air cleaners) and air washers are known as apparatus for removing unwanted materials from air. Air purifiers (air cleaners) are apparatuses that primarily depend on air purifying filters (air filters) for filtering off unwanted materials in air such as suspended fine particles (e.g. dust) on which gaseous contaminants, fats/oils and microorganisms such as bacteria are occasionally deposited. Air washers are apparatus which typically involve the washing of air with water to remove dirt/dust particles, microorganisms, etc. from air.
The first mentioned air purifying filters are available in various types which have been developed to suit specific factors such as the material to be removed, its particle size and the efficiency of particle capture. The filters are also available in various shapes including mats, wedges, fold-ins, baskets, bags, panels and boxes. However, single use of the conventional air purifying filters has been unable to achieve complete removal of air-borne microorganisms such as molds, bacteria and fungi. Further, the microorganisms captured on the filters are difficult to control or kill and may grow on the filters and scatter about to cause secondary contamination; therefore, the existing air purifying filters have not necessarily given satisfactory results in the air purification treatment.
Under the circumstances, the present inventors thought of using enzymes effective in controlling or killing air-borne microorganisms such as mold, bacteria and fungi. Various techniques have so far been proposed as bactericidal/sterilizing or antimicrobial means using enzyme and they include the following.
Japanese Patent Publication No. 21422/1979 discloses a method of controlling microorganisms (e.g. heat-resistant cell spores) in processed food which is characterized in that at least one member of the group consisting of urea, thioglycolic acid and mercaptoethanol, and a bacterial cell wall lysing enzyme are added to the food or starting materials thereof and the mixture is held for a specified time and subsequently heat treated.
Japanese Patent Public Disclosure No. 30584/1989 describes a biocatalyst immobilizing carrier for typical use in the food industry which has a microorganism or an enzyme that work as a biocatalyst immobilized on a carrier together with a lysing enzyme. According to the patent, exemplary microorganisms include Gram-negative bacteria, Gram-positive bacteria, yeasts and molds; useful enzymes are hydrolases such as arnylase, protease and lipase; lysing enzymes include lysozyme, endo-N-acetylmuramidase, endo-N-acetylglucosaminidase, autolysin, ensopeptidase-type bacterial cell wall lysing enzymes, amidase-type bacterial cell wall lysing enzymes, mold cell wall lysing enzymes and yeast cell wall lysing enzymes.
Japanese Patent Public Disclosure No. 5822/1990 discloses an alcoholic preparation for use on raw vegetable which incorporates egg white lysozyme as a natural antimicrobial agent and which has the pH adjusted to be within the range of 2.0-7.0, as well as a modifier for use on raw vegetable which incorporates an organic acid and an organic acid salt or a phosphate salt, has the pH adjusted to be within the range of 2.0-7.0 and also incorporates egg white lysozyme as an antimicrobial agent.
Japanese Patent Public Disclosure No. 23856/1990 discloses a food preservation method which, for the purpose of effectively preventing putrefaction and deterioration of food, adds a polyglycerin fatty acid ester, lysozyme and protamine to the food being produced.
Japanese Patent Publication No. 22144/1991 describes a method of food sterilization which comprises allowing a lysing enzyme such as lysozyme, kinase or xcex2-1,6-glucanase to act upon food and then subjecting it to an ultrasonic treatment.
Japanese Patent Public Disclosure No. 76362/1993 describes a process for producing lysozyme-containing particles which comprises the steps of applying a spray of an aqueous lysozyme slurry into the reaction chamber of a fluidized-bed reactor together with the core particles of a hydratable substance, evaporating the residual water so that the dry lysozyme coating will remain on the particulate core substance, to thereby provide lysozyme-containing particles. The patent teaches that the thus produced lysozyme-containing particles are useful in various kinds of foods, cosmetics, medicines and other applications.
Japanese Patent Public Disclosure No. 276910/1993 discloses a food preservative characterized by the combination of protamine with at least one substance selected from the group consisting of lysozyme, an antimicrobial substance extracted from licorice, vitamin B1 ester and a polyphosphate salt.
Japanese Patent Public Disclosure No. 217749/1994 discloses a food preservative which comprises a caprylic acid monoglyceride and/or a capric monoglyceride in combination with glycine, sodium acetate, lysozyme and an organic acid or an alkali salt thereof, as well as a food preservative which comprises a caprylic acid monoglyceride and/or a capric monoglyceride in combination with glycine, sodium acetate, lysozyme and polyphosphate salt. The patent also teaches that although lysozyme is said to have a lysing effect, its effectiveness is limited to some microbial strains and it cannot be claimed as a practically feasible bacteriostat if used alone.
Japanese Patent Public Disclosure No. 246157/1994 discloses a cell adsorber which has the denatured product of a protein such as lysozyme, avidin or trypsin immobilized on a water-insoluble carrier. According to the patent, cells can be effectively separated or removed from a cell-containing solution by using the cell adsorber.
Japanese Patent Public Disclosure No. 236479/1995 discloses the lysozyme binding of an antimicrobial compound selected from among plant-derived antimicrobial compounds (e.g. perillaldehyde, cinnamaldehyde, salicylaldehyde, anisaldehyde, benzaldehyde and vanillin), antibiotics, synthetic antimicrobial agents, etc. The patent teaches that lysozyme bound to these antimicrobial compounds is useful in medicines, quasi-drugs, foods, etc.
There have also been proposed various inorganic antimicrobial materials which have antimicrobial metals such as silver, zinc and copper supported on inorganic carriers. Examples are inorganic antimicrobial agents having silver, zinc and other ions supported on zeolite through ion-exchange, inorganic antimicrobial agents having metallic silver supported on calcium phosphate through adsorption, inorganic antimicrobial agents having silver ions supported on zirconium phosphate through ion-exchange, and inorganic antimicrobial agents having silver complex salts supported on amorphous silicon oxide through occlusion; these inorganic antimicrobial materials are applied to fibers, plastics, films, paints and various other products (ZEOLITE, vol. 13 No. 2 (1966), pp. 56-63).
Various carriers have also been proposed for use in immobilizing the aforementioned enzymes and they include the following.
Japanese Patent Public Disclosure No. 48825/1974 describes the use of phenolic and aliphatic amine-based ion-exchange resins as carriers for immobilizing egg white lysozyme.
Japanese Patent Public Disclosure No. 48080/1984 discloses the use of platinum coated with Amberlite or aminated polyvinyl alcohol and the like for complex immobilizing of more than one enzyme.
Japanese Patent Public Disclosure No. 49795/1985 discloses the use of nonwoven carriers composed of natural fibers or chemical fibers or mixtures thereof in the web for immobilization treatment of bactericidal lysing enzymes.
Japanese Patent Public Disclosure No. 30584/1989 teaches a column composed of ceramic honeycomb structures, a membrane, particles or a porous body as biocatalyst immobilizing carrier and one which is formed of cordierite is specifically described.
Japanese Patent Public Disclosure No. 256388/1989 teaches the use of an anion-exchange resin as a carrier for supporting inulin-D-fructotransferase.
Japanese Patent Public Disclosure No. 39239/1990 discloses the use of a porous anion-exchange resin as an enzyme immobilizing carrier which has either primary amino groups or secondary amino groups or both as exchange groups.
Japanese Patent Public Disclosure No. 41166/1990 teaches that a porous membrane, fibers or spun yams of ceramics, glass or organic polymers, as well as nets formed by knitting such fibers or spun yarns or particles thereof are suitable as enzyme-immobilizing carriers.
Japanese Patent Public Disclosure No. 269362/1991 teaches the use of lattices as carriers in immunological assay reagents.
Japanese Patent Public Disclosure No. 91117/1994 discloses an air purifier having both a slime bacterial filter and a filter based on an antimicrobial polymer. The patent also teaches the typical use of polyurethane forms, polyethylene, polystyrene, polyacrylamides and/or various photocrosslinkable or photocurable synthetic polymers as the base for immobilizing slime bacteria produced lysing enzymes and antibiotics.
As outlined above, it has been proposed in various fields such as food, medicines and cosmetics that enzymes, for example, those having a lysing action as exemplified by lysozyme be used in solution for bactericidal, antimicrobial, preservative, antimold and other purposes.
However, no technical means has ever been proposed in the art that is based on the idea that an air purifying filter made of a specified material can be enhanced in its ability to control, kill or otherwise remove microorganisms by combining the filter with the above-mentioned enzymes having a lysing action.
The present inventors conducted intensive studies by making approaches from various viewpoints in order to enhance the ability of an air purifying filter to control, kill or otherwise remove microorganisms by using it in combination with a lysing enzyme either alone or in the copresence of various proteins, peptides, polysaccharides, etc. As a result, the inventors found that by immobilizing enzymes on the surfaces of carriers which are made of specified materials and which have specified shapes, the ability of the air purifying filter to control, kill or otherwise remove microorganisms could be enhanced and maintained for a prolonged period. The present invention has been accomplished on the basis of this finding.
The invention provides an air purifying filter having an enzyme immobilized on the surface of a carrier.
The invention also provides an air purifying filter having a large amount of enzyme immobilized on the surfaces of a non-water repellent carrier, such as boron-silica glass fibers through covalent bonding and/or ionic bonding.
The invention further provides an air purifying filter which has a large amount of enzyme immobilized on a HEPA filter through covalent bonding and/or ionic bonding, said HEPA filter being based on non-water repellent microfine boron-silica glass fibers having a diameter of no more than 4 xcexcm.
The invention also provides an air purifying filter having a large amount of enzyme dispersed and immobilized on the surfaces of radical-having ion-exchange fibers through ionic bonding.
Further in addition, the invention provides an air purifying filter characterized on that a large amount of enzyme is dispersed and immobilized, through ionic bonding, on the surfaces of boron-silica glass fibers coated with a polymer having radicals or functional groups.
In another general aspect, an air purifying filter includes a modified enzyme immobilized on a surface of a carrier. The modified enzyme has been modified with a bonding agent that improves bonding. The surface of the carrier has not been rendered to be water repellant prior to immobilizing the modified enzyme on the surface of the carrier. The bonding agent improves bonding of the modified enzyme to the carrier.
Embodiments of the air purifying filter include one or more of the following features. For example, the filter may be used as a HEPA filter. The bonding may include covalent bonding. The carrier may include one or more fibers, such as glass fibers, including boron-silica glass fibers; cellulose fibers, including rayon fibers; and ion-exchange fibers. The fibers may be coated with a polymer having a functional group. The polymer having a functional group may be a polymer having at least one functional group selected from among xe2x80x94NHR (R is not H but an alkyl group selected from among methyl, ethyl, propyl and butyl), xe2x80x94NH2, xe2x80x94C6H5NH2, xe2x80x94COOH and xe2x80x94OH. The modified enzyme may bond to the functional group of the polymer.
The modified enzyme may be immobilized through covalent bonding. The modified enzyme may be either of a single type or a system consisting of two or more types, or it may form a mixture or a compound with a non-enzyme protein, a peptide, and/or a polysaccharide. The enzyme may include at least one lysing enzyme selected from among lysozyme, chitinase, protease, glucose oxidase, glucanase, xcex2-galactosidase, endo-xcex2-N-acetylgluco-saminidase and endolysin. The non-enzyme protein or peptide may be either one bactericidal protein or peptide selected from among protamine, lactoferrin and polylysine. The polysaccharide may be either one of glucan, dextran, mannan, galactomannan, laminaran, carrageenan and agarose.
The modified enzyme may be an enzyme bonded with bromine-N-substituted carbamate; an enzyme bonded with bromine-N-substituted imido carbonate; an enzyme bonded with acetyl cellulose bromide; an enzyme N substituted isourea bromide having the formula of 
an enzyme N substituted imidocarbonyl dibromide having the formula of 
an enzyme N substituted carbamyl bromide having the formula of 
an enzyme substituted acetyl cellulose bromide having the formula of 
an enzyme substituted glutal aldehyde having the formula of 
and a mixture of any one or more of the above compounds including, for example, xcex2-1,3-glucanase substituted acetyl cellulose bromide, lysozyme substituted acetyl cellulose bromide, and neutral protease substituted acetyl cellulose bromide.
In another general aspect, an air purifying filter is fabricated by providing a carrier that has not been rendered to be water repellant; providing an enzyme that has been modified with a bonding agent that improves the bonding to the carrier; and immobilizing the enzyme on a surface of the carrier.
The method of fabricating the air purifying filter may include one or more of the features described herein. For example, the carrier may include one or more fibers and the bonding may be covalent bonding. The enzyme may include a mixture of xcex2-1,3-glucanase substituted acetyl cellulose bromide, lysozyme substituted acetyl cellulose bromide, and neutral protease substituted acetyl cellulose bromide.
In another general aspect, an air purifying filter is used to purify air by providing an air filter, placing the air filter in an air handling system, and passing air through the air filter. The air purifying filter includes a modified enzyme immobilized on a surface of a carrier. The modified enzyme has been modified with a bonding agent that improves bonding, the surface of the carrier has not been rendered to be water repellant prior to immobilizing the modified enzyme on the surface of the carrier, and the bonding agent improves bonding of the modified enzyme to the carrier;
The method of purifying the air may include one or more of the features described herein. For example, the air may be purified of one or more of bacillus subtilis, bacillus cereus, and bacillus anthracis. The modified enzyme may include a mixture of xcex2-1,3-glucanase substituted acetyl cellulose bromide, lysozyme substituted acetyl cellulose bromide, and neutral protease substituted acetyl cellulose bromide.